Wave Action 14.3

1. Wave Action 14.3

2. Wave Characteristics • Size of a wave depends on the strength of the wind and on the length of time it blows. • Wavelength is the distance from crest to the next crest on the wave • Frequency is the number of waves that pass a point in a given period of time. • As wavelength decreases, frequency increases • Wave height or amplitude is what determines wave strength. (distance from crest to trough)

3. Wave changes near shore • Water particles in waves move in small circles in place – wave moves on by • As wave nears shore, waves drag on sloping ocean floor, slowing down bottom of wave • Wave height increases and wavelength decreases as they get close to shore. • Eventually the crest of the wave topples over forming a breaker • Wave surges up beach, gravity slows it, and it flows back out to sea

4. How waves affect shore • Longshore drift – due to waves, water hits shoreline at an angle, carrying sand grains. Water and sand then rush back out to sea at an angle that reflects the original angle • As sand is carried out to sea it is deposited nearby, forming a sand bar • Rip currents are formed when water moving out to sea cuts through the sand bar, forming very strong localized currents as water goes back out to sea ( swim across rip current, not against it.)

5. Beach Erosion • Waves shape beaches by eroding in some places and building it up in other places. • Longshore drift moves sand along the coast and deposits it elsewhere • Barrier islands protect coastlines from force of waves during storms, thereby preventing erosion on mainland. • Sand dunes are held in place by roots of sea grass that grows on them. • Groins prevent erosion in one place but increase erosion further down the beach.